The present invention relates to a method of measuring characteristics of a head employed in a data storage device and relates to the data storage device itself.
As data storage devices, devices employing various kinds of media such as an optical disk and a magnetic tape are known. One of the data storage devices is a hard disk drive (HDD), which is widely used and popular as a device for storing computer data. As a matter of fact, the HDD is one of storage devices indispensable to the contemporary computer systems. In addition, the number of HDD applications has been increasing more and more by virtue of its excellent characteristics. Examples of the HDD applications include not only computer systems, but also moving-picture recording/reproduction devices, car navigation systems, and digital cameras. These examples each employ a removable memory.
A magnetic disk employed in an HDD has a plurality of tracks formed as concentric circles. Each of the tracks is used for recording servo patterns and user data. A magnetic head made of a thin-film device makes an access to a desired area (or to be more specific, a desired address) in accordance with the servo patterns in order to write data into the area or read out data from the area. In an operation to read out data from the magnetic disk, a signal read out by the magnetic head from the disk is subjected to predetermined processing such as a wave-reshaping process and a decoding process in a signal-processing circuit before being supplied to a host. By the same token, data received from the host as data to be stored onto the magnetic disk is also subjected to predetermined processing in the signal-processing circuit before being stored onto the magnetic disk.
As described above, each of the tracks comprises a user-data area for storing user data and a servo area for storing the servo patterns. The servo area has servo data such as a cylinder ID (Gray Code) and a burst pattern. A cylinder ID is the address of the track. The burst pattern includes relative-position information in the magnetic head as information with respect to the track. The servo patterns are created in a plurality of sectors on a track. Sectors on a track are separated from each other in the circular-circumferential direction of the track. In the circular-circumferential direction, the positions (or the phases, so to speak) of servo patterns in sectors are uniform over all the tracks. With the magnetic disk put in a rotating state, operations to read out data from the disk and write data onto the disk are carried out while verifying the position of the magnetic head on the basis of the servo patterns.
Servo patterns are written onto the magnetic disk at the factory before an HDD employing the magnetic disk is shipped to the customer as a product. A typical conventional operation to write servo patterns onto a magnetic disk is carried out by a servo writer serving as an external apparatus. With a top cover of the HDD removed from the HDD, the HDD is set on the servo writer. The servo writer then uses a positioner also referred to as an external positioning mechanism to determine the position of the magnetic head in the HDD before writing servo patterns generated by a servo-pattern generation circuit onto the magnetic disk.
At the present time, the cost of carrying out a servo-track write (STW) process is a big portion of the cost to manufacture an HDD. Particularly in recent years, competition to increase the storage capacity of an HDD has been becoming fierce and, accompanying the competition, a TPI (Tracks Per Inch) has been increasing. As the TPI increases, the number of tracks rises and the track width decreases. The increased TPI and the decreased track width raise the STW process time and require high precision of the servo writer. The rising STW process time and the high precision of the servo writer in turn increase the cost of the STW process. In order to lower the cost of the STW process, the cost of the servo writer and the time of the STW process must be reduced to mention a few. As an example, unlike the conventional STW process, typically, an SSW (Self Servo Write) process is carried out to write servo patterns onto the magnetic disk with the top cover placed on the HDD as it is. In the SSW process, as the mechanical portion, only the main body of the HDD is used, and an external circuit is used as a circuit for controlling a spindle motor (SPM) and a voice coil motor (VCM), which are employed in the HDD as motors for writing servo patterns onto the magnetic disk. In this way, the cost of the servo writer can be lowered.
A typical SSW process is disclosed in documents such as patent document 1 (Japanese Patent Laid-Open No. 2004-963043). In this SSW process, position detection patterns for detecting a position in the rotational direction are recorded onto one face of the magnetic disk in advance. The position detection patterns are clock patterns recorded at predetermined intervals in the circumferential direction. A servo writer carries out an operation to pre-write the clock patterns for each magnetic disk. Then, a magnetic disk completing a pre-write process is mounted on an HDD.
The STW process disclosed in patent document 1 is carried out to write servo patterns onto a magnetic disk completing a pre-write process to record clock patterns on the disk in advance. In an initial sequence, the head is positioned on the innermost circumference of the magnetic disk to write servo patterns onto the disk as reference patterns. Then, sequentially, a recorded servo pattern is used to determine the position of a write element. In an operation to write servo patterns onto the magnetic disk, the clock patterns recorded on the entire face of the disk are used as references to carry out an operation to set timings to write the servo patterns. Thus, it is possible to prevent clocking precision from deteriorating due to effects of an increased frequency of the servo patterns and rotation jitters of the magnetic disk. By the clocking precision, the precision of an operation to set write timings is implied.